drm/amd/display: Use freesync when `DRM_EDID_FEATURE_CONTINUOUS_FREQ` found

drm/amd/display: Use freesync when `DRM_EDID_FEATURE_CONTINUOUS_FREQ` found

The monitor shipped with the Framework 16 supports VRR [1], but it's not
being advertised.

This is because the detailed timing block doesn't contain
`EDID_DETAIL_MONITOR_RANGE` which amdgpu looks for to find min and max
frequencies.  This check however is superfluous for this case because
update_display_info() calls drm_get_monitor_range() to get these ranges
already.

So if the `DRM_EDID_FEATURE_CONTINUOUS_FREQ` EDID feature is found then
turn on freesync without extra checks.

v2: squash in fix from Harry

Closes: https://www.reddit.com/r/framework/comments/1b4y2i5/no_variable_refresh_rate_on_the_framework_16_on/
Closes: https://www.reddit.com/r/framework/comments/1b6vzcy/framework_16_variable_refresh_rate/
Closes: https://community.frame.work/t/resolved-no-vrr-freesync-with-amd-version/42338
Link: https://gist.github.com/superm1/e8fbacfa4d0f53150231d3a3e0a13faf
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>